1. Field Of The Invention
The invention relates to a process for the production of 6-hydroxynicotinic acid by the enzymatic hydroxylation of nicotinic acid.
2. Prior Art
Several methods are known for the production of 6-hydroxynicotinic acid by means of organic synthesis. For example, 6-hydroxynicotinic acid can be obtained from 2-pyridone by the Kolbe-Schmidt type carboxylation of hydroxy aromatics. Other syntheses start out from maleic acid or isocinchomeronic acid [Briancourt et al., J. Chim. Ther. (1973), 8 (2) 226-32; Quarroz, Swiss Application No. 7731/80]. However, none of such synthesis permit a simple, inexpensive and favorable-to-the-environment type of production of pure 6-hydroxynicotinic acid. Such processes have the disadvantage that the conversion is not quantitative and undesirable by-products accompany the reaction. The by-products represent contamination which must be removed from the reaction product after reaction is completed.
It is also known that microorganisms of the variety Bacillus, Pseudomonas, Clostridium, Sarcina and Mycobacterium grew on nicotinic acid and that they use such substrate as a source of carbon, nitrogen and energy [Allison, M. J. C., J. Biol. Chem. (1943) 147, 785; Behrman, E. J., and Stanier, R. V., J. Biol. Chem. (1957) 228, 923]. In the case of all of such studied organisms, the nicotinic acid is oxidized to 6-hydroxynicotinic acid in the first decomposition step. The 6-hydroxynicotinic acid is further immediately converted, and without significant enrichment, in the case of aerobic organisms, to water, carbon and ammonia.
After break up of the microorganism, it is possible to isolate the nicotinic acid hydroxylase into more or less pure form [Hunt, A. L., Biochem. J. (1958) 72, 1-7]. The nicotinic acid hydroxylases are large molecules of approximately 400,000 dalton. They contain flavin cofactors, many metal atoms (Fe, Mo), inorganic sulfur and in some cases even selenium. The nicotinic acid hydroxylases are active only in the presence of suitable electron transmitting systems (for example, cytochrome, flavins, NADP.sup.+ and others). The nicotinic acid hydroxylase can be isolated from cell extracts and the enzyme preparations can be used for the hydroxylation of nicotinic acid. Such has been done and small quantities of 6-hydroxynicotinic acid were actually obtained [Behrman and Stanier, J. Biol. Chem. (1957) 228, 923]. Apart from the high costs of enzyme isolation and of the instability of the nicotinic acid hydroxylase, it was still necessary to take care of the regeneration of cofactors and electron transmitting systems.